John Walker's Fourmilab Change Log

Monday, September 28, 2015

Total Lunar Eclipse 2015-09-28

Here is an animation of the eclipse from the start through mid-totality.

These images were taken with a Nikon D600 camera and a 25 year old Nikon 300 mm f/4.5 lens. All exposures were made with a lens aperture of f/8 and ISO sensitivity of 200. Exposures prior to totality used a shutter speed of 1/125 second, allowing you to see how the Moon darkened as it entered the penumbra. The shot at the start of totality (where the lower limb of the Moon is quite bright) used a shutter speed of 1/4 second, while the remaining two images of totality used a one second exposure.

I have aligned, rotated, and stacked the images while preparing the animation with The Gimp, taking out the apparent rotation of the Moon due to the Earth's rotation as the eclipse progressed.

Posted at
17:03

Monday, September 21, 2015

Reading List: Sacramento's Moon Rockets

In 1849 gold was discovered in California, setting off a gold rush which
would bring a wave of prospectors and fortune seekers into one of the
greatest booms in American history. By the early 20th century, the grizzled
prospector panning for gold had given way to industrial extraction of
the metal. In an age before anybody had heard the word “environmentalism”,
this was accomplished in the most direct way possible: man made lakes were
created on gold-bearing land, then a barge would dredge up the bottom and
mix it with mercury, which would form an amalgam with the gold. The gold
could later be separated, purified, and sold.

The process effectively destroyed the land on which it was used. The
topsoil was ripped out, vegetation killed, and the jumbled remains after
extraction dumped in barren hills of tailings. Half a
century later, the mined-out land was considered unusable for either
agriculture or residential construction. Some described it as a
“moonscape”.

It was perhaps appropriate that, in the 1960s, this stark terrain became
home to the test stands on which the upper stage of NASA's Saturn
rockets were developed and tested before flight. Every Saturn upper
stage, including those which launched Apollo flights to the Moon,
underwent a full-duration flight qualification firing there before
being shipped to Florida for launch.

When the Saturn project was approved, Douglas Aircraft Company
won the contract to develop the upper stage, which would be powered by
liquid hydrogen and liquid oxygen (LH2/LOX) and have the ability to restart in
space, allowing the Apollo spacecraft to leave Earth orbit on a trajectory
bound for the Moon. The initial upper stage was called the
S-IV, and was used as the
second stage of the Saturn I
launcher flown between 1961 and 1965 to demonstrate heavy lift
booster operations and do development work related to the Apollo project.
The S-IV used a cluster of six RL10
engines, at the time the largest operational LH2/LOX engine. The Saturn I had
eight engines on its first stage and six engines on the S-IV. Given the
reliability of rocket engines at the time, many engineers were dubious of
getting fourteen engines to work on every launch (although
the Saturn I did have a limited engine out capability). Skeptics called it
“Cluster's last stand.”

The S-IV stages were manufactured at the Douglas plant in Huntington Beach,
California, but there was no suitable location near the plant where they could
be tested. The abandoned mining land near Sacramento had been acquired by Aerojet
for rocket testing, and Douglas purchased a portion for its own use.
The outsized S-IV stage was very difficult to transport by road, so the ability to
ship it by water from southern California to the test site via San Francisco
Bay and the Sacramento River was a major advantage of the location.

The operational launchers for Apollo missions would be the
Saturn IB
and Saturn V,
with the Saturn IB used for Earth orbital missions and the
Saturn V for Moon flights and launching space stations. An
upgraded upper stage, the
S-IVB, would be
used by these launchers, as the second stage of the Saturn IB and
the third stage of the Saturn V. (S-IVBs for the two launchers
differed in details, but the basic configuration was the same.)
The six RL-10 engines of the S-IV were replaced by a single much more
powerful
J-2 engine
which had, by that time, become available.

The Sacramento test facility was modified to do development and
preflight testing of the S-IVB, and proceeded to test every flight
stage. No rocket firing is ever routine, and in 1965 and 1967
explosions destroyed an S-IV test article and a flight S-IVB
stage which was scheduled to be used in
Apollo 8.
Fortunately, there were no casualties from these spectacular
accidents, and they provided the first data on the
effects of large scale LH2/LOX explosions which proved to be
far more benign than had been feared. It had been predicted
that a LH2/LOX explosion would produce a blast equal to 65% of
the propellant mass of TNT when, in fact, the measured blast was
just 5% TNT equivalent mass. It's nice to know, but an expensive way
to learn.

This book is not a detailed history of the Sacramento test facility but
rather a photo gallery showing the construction of the site;
transportation of stages by sea, road, and later by the amazing
Super Guppy
airplane; testing of S-IV and S-IVB stages; explosions and their aftermath;
and a visit to the site fifty years later. The photos have well-researched and
informative captions.

When you think of the Apollo program, the Cape, Houston, Huntsville, and
maybe Slidell come to mind, but rarely Sacramento. And yet every Apollo
mission relied upon a rocket stage tested at the Rancho Cordova site
near that city. Here is a part of the grandiose effort to go to the Moon
you probably haven't seen before. The book is just 96 pages and expensive
(a small print run and colour on almost every page will do that), but
there are many pictures collected here I've seen nowhere else.

Monday, September 14, 2015

Reading List: Mud: A Military History

Military historians from antiquity to the present day have examined
innumerable aspects of human conflict in painstaking detail: strategy,
tactics, morale, terrain, command structures, training of troops,
logistics, mobility, weapons, armour, intelligence both before
the battle and after the enemy is engaged, and a multitude of other
factors which determine the outcome of the engagement. If you step
back from the war college or general staff view from above and ask
the actual combatants in land warfare, from privates to flag rank,
what they often recall as dominating their contemporary memories, it
will often be none of these things, but rather mud. This
is the subject of this slim (190 page) but extensively researched
and documented book.

When large numbers of men, equipment, and horses (or, in the modern era,
mechanised vehicles) traverse terrain, unless it is totally dry,
it is likely to be stirred up into a glutinous mix of soil and
water: mud. The military mind cannot resist classifying things, and
here the author draws the distinction between Type I mud, which is
“bottomless” (well, not really, of course, but effectively
so since it is deep enough to mire and swallow up any military
force which attempts to cross it), Type IIa, which is dominated by
liquid and can actually serve to clean hardware which passes through it
but may make it impossible to dig trenches or build fortifications,
and Type IIb, which is sticky and can immobilise and render ineffective
everything from an infantryman's entrenching tool to a main battle tank.

The book illustrates the impact of mud on land warfare, examining its
effects on engineering works such as building roads and
fortifications, morale of troops, health, and wear and tear and
reliability of equipment. Permanent mud (as exists in marshes and
other wetlands), seasonal mud (monsoons and the horrific autumn rain
and spring thaw mud in Russia which brought both Napoleon and Hitler's
armies to a standstill), and random mud (where a downpour halts an
advance as effectively as enemy action) each merit their own
chapters.

Technical discussions of the composition and behaviour of mud and
its effects upon soldiers and military equipment are illustrated
by abundant examples from conflicts from antiquity to the most recent
war in Iraq. Most examples date from the era of mechanised warfare,
but the reader will rapidly appreciate that the reality of mud to
the infantryman has changed little since the time of Thucydides.

In Cat's Cradle, Kurt Vonnegut
has one of his characters asked to solve one of the greatest problems
facing Marines in combat: mud. The solution,
ice-nine,
is fantasy, but generations of Marines would probably agree upon
the primacy of the problem. Finally the importance of mud in
military affairs gets its due in this book. One hopes military planners will
not ignore it, as so many of their predecessors have with disastrous
consequences.

Posted at
01:16

Saturday, September 5, 2015

Reading List: The Singular Universe and the Reality of Time

In his 2013 book Time Reborn
(June 2013), Lee Smolin argued that, despite its extraordinary
effectiveness in understanding the behaviour of isolated systems, what
he calls the “Newtonian paradigm” is inadequate to
discuss cosmology: the history and evolution of the universe as a
whole. In this book, Smolin and philosopher Roberto Mangabeira Unger
expand upon that observation and present the case that the current
crisis in cosmology, with its appeal to multiple universes and
mathematical structures which are unobservable, even in principle, is
a consequence of the philosophical, scientific, and mathematical tools
we've been employing since the dawn of science attempting to be used
outside their domain of applicability, and that we must think
differently when speaking of the universe as a whole, which contains
all of its own causes and obeys no laws outside itself. The authors
do not present their own theories to replace those of present-day
cosmology (although they discuss the merits of several proposals), but
rather describe their work as a “proposal in natural
philosophy” which might guide investigators searching for those
new theories.

In brief, the Newtonian paradigm is that the evolution of physical
systems is described by differential equations which, given a set of
initial conditions, permit calculating the evolution of a system
in the future. Since the laws of physics at the microscopic
level are reversible, given complete knowledge of the state of a system
at a given time, its past can equally be determined. Quantum
mechanics modifies this only in that rather than calculating the
position and momentum of particles (or other observables), we
calculate the deterministic evolution of the wave function which
gives the probability of observing them in specific states in the future.

This paradigm divides physics into two components: laws (differential
equations) and initial conditions (specification of the initial state
of the system being observed). The laws themselves, although they
allow calculating the evolution of the system in time, are themselves
timeless: they do not change and are unaffected by the interaction of
objects. But if the laws are timeless and not subject to back-reaction
by the objects whose interaction they govern, where did they come
from and where do they exist? While conceding that
these aren't matters which working scientists spend much time
thinking about, in the context of cosmology they post serious
philosophical problems. If the universe all that is and contains
all of its own causes, there is no place for laws which are outside
the universe, cannot be acted upon by objects within it, and have
no apparent cause.

Further, because mathematics has been so effective in expressing the
laws of physics we've deduced from experiments and observations,
many scientists have come to believe that mathematics can be a
guide to exploring physics and cosmology: that some mathematical
objects we have explored are, in a sense, homologous to the universe,
and that learning more about the mathematics can be a guide to
discoveries about reality.

One of the most fundamental discoveries in cosmology, which has
happened within the lifetimes of many readers of this book,
including me, is that the universe has a history. When
I was a child, some scientists (a majority, as I recall) believed
the universe was infinite and eternal, and that observers at any
time in the past or future would observe, at the largest scales,
pretty much the same thing. Others argued for an origin at a finite
time in the past, with the early universe having a temperature
and density much greater than at present—this theory was
mocked as the “big bang”. Discovery of the cosmic
background radiation and objects in the distant universe which
did not at all resemble those we see nearby decisively decided
this dispute in favour of the big bang, and recent precision
measurements have allowed determination of when it happened and
how the universe evolved subsequently.

If the universe has a finite age, this makes the idea of
timeless laws even more difficult to accept. If the universe is
eternal, one can accept that the laws we observe have always been
that way and always will be. But if the universe had an origin we
can observe, how did the laws get baked into the universe? What
happened before the origin we observe? If every event has a cause,
what was the cause of the big bang?

The authors argue that in cosmology—a theory encompassing
the entire universe—a global privileged time must govern
all events. Time flows not from some absolute clock as envisioned
by Newtonian physics or the elastic time of special and general
relativity, but from causality: every event has one or more causes,
and these causes are unique. Depending upon their position and state
of motion, observers will disagree about the durations measured
by their own clocks, and on the order in which things
at different positions in space occurred (the relativity of
simultaneity), but they will always observe a given event to have the
same cause(s), which precede it. This relational notion of time,
they argue, is primordial, and space may be emergent from it.

Given this absolute and privileged notion of time (which many
physicists would dispute, although the authors argue does not
conflict with relativity), that time is defined by the
causality of events which cause change in the universe, and that
there is a single universe with nothing outside it and which contains all
of its own causes, then is it not plausible to conclude that the
“laws” of physics which we observe are not timeless
laws somehow outside the universe or grounded in a Platonic mathematics
beyond the universe, but rather have their own causes, within the
universe, and are subject to change: just as there is no “unmoved
mover”, there is no timeless law? The authors, particularly
Smolin, suggest that just as we infer laws from observing
regularities in the behaviour of systems within the universe
when performing experiments in various circumstances, these laws
emerge as the universe develops “habits” as interactions
happen over and over. In the present cooled-down state of the
universe, it's very much set in its ways, and since everything has
happened innumerable times we observe the laws to be unchanging. But
closer to the big bang or at extreme events in the subsequent universe,
those habits haven't been established and true novelty can occur.
(Indeed, simply by synthesising a protein with a hundred amino acids
at random, you're almost certain to have created a molecule which has
never existed before in the observable universe, and it may be harder
to crystallise the first time than subsequently. This appears to
be the case. This is my observation, not the authors'.)

Further, not only may the laws change, but entirely new kinds of
change may occur: change itself can change. For example, on
Earth, change was initially governed entirely by the laws
of physics and chemistry (with chemistry ultimately based upon
physics). But with the emergence of life, change began to be
driven by evolution which, while at the molecular level was
ultimately based upon chemistry, created structures which
equilibrium chemistry never could, and dramatically changed the
physical environment of the planet. This was not just change, but
a novel kind of change. If it happened here, in our own recent
(in cosmological time) history, why should we assume other novel
kinds of change did not emerge in the early universe, or will not
continue to manifest themselves in the future?

This is a very difficult and somewhat odd book. It is written in two
parts, each by one of the co-authors, largely independent of one another.
There is a twenty page appendix in which the authors discuss their
disagreements with one another, some of which are fundamental.
I found Unger's part tedious, repetitive, and embodying all of things
I dislike about academic philosophers. He has some important things
to say, but I found that slogging through almost 350 pages of it was
like watching somebody beat a moose to death with an aluminium
baseball bat: I believe a good editor, or even a mediocre one, could
have cut this to 50 pages without losing anything and making the
argument more clearly than trying to dig it out of this blizzard
of words. Lee Smolin is one of the most lucid communicators among
present-day research scientists, and his part is clear, well-argued,
and a delight to read; it's just that you have to slog through the
swamp to get there.

While suggesting we may have been thinking about cosmology all wrong,
this is not a book which suggests either an immediate theoretical or
experimental programme to explore these new ideas. Instead, it
intends to plant the seed that, apart from time and causality,
everything may be emergent, and that when we think about
the early universe we cannot rely upon the fixed framework of our
cooled-down universe with its regularities. Some of this is obvious
and non-controversial: before there were atoms, there was no periodic
table of the elements. But was there a time before there was
conservation of energy, or before locality?